Electrical motors and methods thereof having reduced electromagnetic emissions

ABSTRACT

Motors and method of operation thereof operable in a running mode wherein the motor operates at a constant speed, and operable in a park mode wherein the motor is dynamically parked. The motor is housed within a housing and includes a rotating park disk configured to cause the motor to dynamically park. A park wire electrically couples the park disk to a switch configured to selectively set the motor to the running mode or the park mode, and a power wire electrically couples the park disk to a power source. Portions of the wires exit the housing so as to be disposed externally of the housing. The park wire is electrically isolated from the power wire during operation of the motor in the running mode and the park wire is electrically connected to the power wire during operation of the motor in the park mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/986,745, filed Nov. 19, 2013, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to electric motors. More particularly, this invention relates to electric motors of types that are adapted to drive windshield wipers and incorporate a dynamic park capability.

The motor vehicle industry utilizes electric motors to drive windshield wipers. An exemplary 24 volt direct current (DC) windshield wiper motor 10 as known in the art is represented in FIG. 1.

As conventional in the art, the motor 10 may be controlled, generally by a manual selector switch (not shown), to be operable in any one of three possible modes of operation: park, high speed, and low speed. The motor 10 incorporates a park disk 12 for what is known and referred to as dynamic parking. The park disk 12 is rotatably mounted within a gear head 13, rotates as a result of engaging a worm gear 15 driven by a rotor (not shown) within an electric motor housing 11 of the motor 10, and drives a mechanism functionally coupled to a windshield wiper (not shown). The park disk 12 is a circular disk-shaped component that includes a ground tab 14, park section 16, and battery positive section 18. FIG. 2 represents an interior portion of a gear housing plate 20 that is configured to be assembled to the gear head 13 for interaction with the park disk 12 of FIG. 1. The gear housing plate 20 has ground, park, and battery positive contacts 22, 24 and 26, respectively, which interact with the ground tab 14, park section 16, and battery positive section 18, respectively, of the park disk 12 as the park disk 12 rotates. FIG. 3A represents a diagram of the park disk 12 as assembled with three armatures corresponding to the ground, park, and battery positive contacts 22, 24 and 26. During operation, when the manual selector switch (motor switch) is set to ‘low’ or ‘high’ speed, the motor 10 operates in low or high speed mode, respectively, and the park disk 12 consequently rotates, an exemplary transient operating position of which is depicted in FIG. 3A. If the switch is moved to ‘park’ while the motor 10 is operating in low or high speed mode, the park disk 12 continues to rotate, for example, through the transient position shown in FIG. 3A, until it reaches a predetermined park position, represented in FIG. 3B. As represented, the park position of the motor 10 is reached when the battery positive contact 26 is no longer electrically connected to positive power via the battery positive section 18 of the park disk 12, and the park contact 16 is electrically connected to the ground contact 14 (battery negative) through the park disk 12, that is, the park contact 24 is in contact with the park section 16 and the ground contact 22 is in contact with the ground tab 14. Once the park disk 12 reaches the park position, the motor 10 functions as a load generator developing a torque that rapidly stops the motor 10 and thereby stops the windshield wipers.

In normal operation, the park disk 12 makes contact to +24 volts and ground once each revolution of the park disk 12 thereby sequentially creating a negative pulse and a positive pulse of conducted and radiated electromagnetic emissions. On dynamic park motors such as the windshield wiper motor 10 of FIG. 1, these pulses occur when the voltage goes from +24 volts to ground (0 volts) and then back to +24 volts. For example, FIG. 4A represents a measurement of pulses taken from a conventional dynamic park motor, such as the motor 10 of FIG. 1, as the park disk rotates. These pulses may travel through wires exiting the motor 10, for example, high input, low input, and park wires, and radiate therefrom causing electro-magnetic interference (EMI) during each revolution of the park disk 12.

Increasingly, electronic devices are installed in or used around motor vehicles which are sensitive to the EMI generated by electric motors. In certain cases, EMI can pose a security risk. For example, the EMI generated by the windshield wiper motor 10 of FIG. 1 can be detected and traced to a military vehicle in which the motor 10 is installed. Consequently, there is a need for systems and methods suitable for reducing or eliminating this pulse of electromagnetic emissions.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides electrical motors and methods of operation thereof suitable for reducing or eliminating a pulse of electromagnetic emissions produced by the electric motors.

According to a first aspect of the invention, an electrical motor is operable in at least one running mode wherein the electrical motor operates at a constant speed, and is operable in a park mode wherein the electrical motor is dynamically parked. The electrical motor is housed within a housing and includes a rotating park disk configured to cause the electrical motor to dynamically park. A park wire electrically couples the park disk to a motor switch configured to selectively set the electrical motor to the at least one running mode or the park mode, and a power wire electrically couples the park disk to a power source. Portions of the park wire and the power wire exit the housing of the electrical motor so as to be disposed externally of the housing. The park wire is electrically isolated from the power wire during operation of the electrical motor in the at least one running mode and the park wire is electrically connected to the power wire during operation of the electrical motor in the park mode.

According to a second aspect of the invention, an electrical motor is operable in at least one running mode wherein the electrical motor operates at a constant speed, and is operable in a park mode wherein the electrical motor is dynamically parked. The electrical motor is housed within a housing and includes a rotating park disk functionally coupled to a ground contact, a park contact, and a battery positive contact disk. The park disk is configured to cause the electrical motor to dynamically park by operating the electrical motor in the at least one running mode until the park disk rotates to a park position such that the park disk is electrically coupled to the ground contact and the park contact and not electrically coupled to the battery positive contact. A park wire electrically couples the park contact to a motor switch configured to selectively operate the electrical motor in the at least one running mode or the park mode, and a battery positive wire electrically couples the battery positive contact to a positive terminal on a battery. Portions of the park wire and the battery positive wire exit the housing of the electrical motor so as to be disposed externally of the housing. The park wire is electrically isolated from the battery positive wire during operation of the electrical motor in the at least one running mode and the park wire is electrically connected to the battery positive wire during operation of the electrical motor in the park mode.

According to a third aspect of the invention, a method of operating an electrical motor that is operable in at least one running mode wherein the electrical motor operates at a constant speed and that is operable in a park mode wherein the electrical motor is dynamically parked. The electrical motor is housed in a housing and includes a rotating park disk configured to cause the electrical motor to dynamically park. A park wire electrically couples the park disk to a motor switch configured to selectively set the electrical motor to the at least one running mode or the park mode, and a power wire electrically couples the park disk to a power source. Portions of the park wire and the power wire exit the housing of the electrical motor so as to be disposed externally of the housing. The method includes electrically isolating the park wire from the power wire during operation of the electrical motor in the at least one running mode, and electrically connecting the park wire to the power wire during operation of the electrical motor in the park mode.

A technical effect of the invention is the ability to greatly reduce or eliminate EMI produced by electric motors, for example, an electric motor operating to drive windshield wipers. Specifically, by electrically isolating the park wire from the power wire, electromagnetic emissions may be, and preferably are, reduced, captured, and suppressed before the emissions can conduct through and radiate from the park and power wires that connect the motor to the motor switch. Electromagnet emissions can potentially be reduced to an extent capable of protecting electronic devices that might otherwise be sensitive to EMI, and/or avoid detection and tracing of the motor or a vehicle in which the motor is installed.

Other aspects and advantages of this invention will be better appreciated from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a windshield wiper motor of a type known in the art wherein the motor is shown partially disassembled to expose a park disk for illustrative purposes.

FIG. 2 represents an interior portion of a gear housing plate having ground, park, and battery positive contacts adapted for interaction with the park disk of FIG. 1.

FIGS. 3A and 3B are diagrams representing a park disk of an electric motor and corresponding ground, park, and battery positive contacts of the types depicted in FIGS. 1 and 2, wherein FIG. 3A represents the park disk in a transient operating position, and FIG. 3B represents the park disk in a park position.

FIGS. 4A and 4B are graphs representing measurements of electromagnetic emissions from, respectively, a conventional electrical motor of a type known in the art and an electrical motor in accordance with an aspect of the invention.

FIG. 5 represents a printed circuit board having components thereon suitable for suppressing EMI produced from an electrical motor in accordance with an aspect of the invention.

FIG. 6 represents an exterior portion of a gear housing plate of an electrical motor of a type known in the art.

FIG. 7 represents the printed circuit board of FIG. 5 as installed on the exterior portion of the gear housing plate of FIG. 6 in accordance with an aspect of the invention.

FIGS. 8 and 9 are wiring diagrams representing circuits suitable for suppressing the EMI of an electric motor in accordance with aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to systems and methods suitable for reducing or eliminating electromagnetic emissions produced by an electric motor, particular but nonlimiting examples of which include dynamic park electric motors used for driving windshield wipers on motor vehicles. The systems described hereinafter reduce the electromagnetic emissions produced by the electric motors during operation by isolating a park wire from the park disk with a relay or a functional equivalent thereof. The emissions are captured and suppressed before they can conduct through and radiate from the wires to the motor switch and the surrounding environment, as represented in FIG. 4B. These systems may be installed during manufacture of the motors or may be installed on motors after manufacture, and provide reduced electromagnetic emissions within industry standards, such as the U.S. military standard MIL-STD-461F. The systems can suppress the emissions with a circuit of components wired directly into a motor's electrical system, and preferably installed externally to the motor without altering or changing any physical characteristics of the motor. This promotes a cost effective solution on electric motors where EMI suppression is needed, a notable but nonlimiting example of which is military vehicles. In the drawings, identical reference numerals denote the same or functionally equivalent elements throughout the various views.

FIG. 5 represents a system including a printed circuit board 30 having components thereon suitable for suppressing electromagnetic emissions produced from an electric motor, such as the motor 10 of FIG. 1, in accordance with an aspect of the invention. FIG. 6 represents an exterior portion of the gear housing plate 20 of FIG. 2, which as previously discussed is adapted for assembly with the +24 volt DC electric motor 10 of FIG. 1. FIG. 7 represents the printed circuit board 30 of FIG. 5 installed on the exterior portion of the gear housing plate 20 of FIG. 6 in accordance with an aspect of the invention. The printed circuit board 30 has located thereon bypass capacitors 32, an RC filter 34 (comprising a resistor and capacitor in parallel), an isolation relay 36, inductors 38, a Faraday cage 40, an EMI filter PC board 42 including EMI filter caps 44, and at least one filter capacitor 46. The bypass capacitors 32, RC filter 34, isolation relay 36, and inductors 38 are preferably electrically connected according to the wiring diagram represented in FIG. 8. It should be understood that the components and wiring of the system disclosed in FIGS. 5 and 8 represent a single embodiment of the invention as directed towards the motor 10, and that other functionally equivalent components and wiring may be used for the motor 10 or other motors. For example, the number and size of the bypass capacitors 32 used in the system may vary depending on the specific motor to which the system is coupled or the application for which it is being used.

As previously stated, during operation of the motor 10 at least one pulse of conducted and radiated electromagnetic emissions may be produced with every complete rotation of the park disk 12. Such pulses may travel through input wires 50 and 52 (for example, low and high input wires 50 and 52) and a park wire 54 that connect the motor switch (“SWITCH” in FIG. 8) to the motor 10, and may then radiate from the wires 50, 52 and 54 and potentially cause EMI. FIG. 8 represents the high input wire 52 and the low input wire 50 traveling from the motor 10 through the optional Faraday cage 40, through a ferrite bead 48, through the inductors 38, and on to the motor switch. Preferably, the system includes the Faraday cage 40, EMI filter PC board 42, EMI filter caps 44, and filter capacitor 46. If included, the high input wire 52 and the low input wire 50 first travel into the Faraday cage 40 that houses the filter capacitors 46 and through the capacitors 46. The Faraday cage 40, capacitors 46, and any other components within the cage 40 act to suppress electromagnetic emissions traveling on the high and low input wires 52 and 50 during operation of the motor 10. The high and low input wires 52 and 50 may then travel out of the Faraday cage 40 and through the EMI filter PC board 42 having EMI filter caps 44 before continuing on to the ferrite bead 48 represented in FIG. 8.

Conventionally, the park wire 54 would be connected to power through the park contact 24 and the park section 16 of the park disk 12 during operation of the motor 10, for example, when the park disk 12 is in the position depicted in FIG. 3A. According to an aspect of the present invention, in order to prevent electromagnetic emissions from traveling through the park wire 54 while the motor 10 is operating, the park disk 12 is electrically isolated from the power (battery positive wire 58) during operation of the motor 10 in high and low speeds with the isolation relay 36, which may be, for example, an electromechanical relay or an equivalent thereof. The isolation relay 36 is configured to be normally open during operation of the motor 10 thereby electrically isolating the park wire 54 from power. When the motor switch is moved to park, the isolation relay 36 is energized, providing power to the low input and park wires 50 and 54 allowing the motor 10 to dynamically park.

In view of the above, the motor 10 functionally coupled to the system operates as follows. When the motor 10 is off and the motor switch is set to the park position, the park disk 12 is in the dynamic park position, that is, the ground contact 22 is in contact with the park disk 12 (for example, as represented in FIG. 3B). When the motor switch is set to either the low or high position (for example, as represented in FIG. 3A), the motor 10 begins running in low or high speed, respectively. While the motor 10 is running in low speed, the high input wire is open. Conversely, when the motor 10 is running in high speed, the low input wire is open. Regardless, when operating in either low speed or high speed, electrical current flows through the corresponding high or low input wire 52 or 50 to a battery negative terminal through a battery negative wire 56. During this time, there is no current flow through the rest of the circuit.

When the motor switch is set back to the park position from either the high position or the low position, the high input wire 52 is open and the low input wire 50 is shorted to the park wire 54 on the motor switch. At this point, the isolation relay 36 is energized and thereby connects the battery positive wire 58 to the park disk 12 through the common and normally open contacts of the isolation relay 36, causing the motor 10 to continue to operate in low speed. Once the park disk 12 rotates to the park position, the isolation relay 36 is de-energized, thereby removing power from the park disk 12 and causing the motor 10 to cease operation.

According to another aspect of the invention, the isolation relay 36 of FIG. 8 may be replaced with a solid-state relay (switch) 60, for example, as represented in a wiring diagram of FIG. 9. The solid-state relay 60 is represented as an optocoupled solid-state relay comprising an optocoupler (opto-isolated triac) 62. FIG. 9 shows RC filters 34 that correspond to the RC filters 34 of FIGS. 5, 7 and 8, and therefore each comprise a resistor and capacitor in parallel with each other. It may be beneficial to also include a metal oxide varistor (MOV) as a surge protector as represented in FIG. 9. FIG. 9 further shows current limiting resistors 66 that limit a trigger current at the output of the optocoupler 62 and gate (TRIAC) 68 of the solid-state relay 60. When the motor 10 is operating in either low or high speed, only a nominal current, for example, less than five milliamperes, will be flowing through the resistors in the RC filters 34. During this time, there is no current flow through the rest of the solid-state relay 60.

When the motor switch is set from either high or low to park, the park wire 54 is connected to the low input wire 50 at the motor switch. This provides power to the input of the optocoupler 62, coupling the TRIAC output of the optocoupler 62 (signal driver) and turning the solid-state relay 60 on. Electrical current then flows from power at the switch through a power lead to the park disk 12 of the motor 10. During this time, there is a nominal current, for example, less than five milliamperes, flowing in the resistors in the RC filters 34, and there is no current flow through the rest of the solid-state relay 60.

While the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, the physical location of the components on the printed circuit board 30 could differ from that shown, functionally equivalent components other than those noted could be used, and the number and size of components used could differ. Therefore, the scope of the invention is to be limited only by the following claims. 

1. An electrical motor operable in at least one running mode wherein the electrical motor operates at a constant speed and operable in a park mode wherein the electrical motor dynamically parks, the electrical motor comprising: a housing; a rotating park disk within the housing and configured to cause the electrical motor to dynamically park; a park wire electrically coupling the park disk to a motor switch, the motor switch configured to selectively switch the electrical motor between the at least one running mode and the park mode, the park wire exiting the housing and being exposed at an exterior of the housing; and a power wire electrically coupling the park disk to a power source, the power wire exiting the housing and being exposed at the exterior of the housing; wherein the park disk is electrically isolated from the power wire during operation of the electrical motor in the at least one running mode and the park wire is electrically connected to the power wire through the park disk during operation of the electrical motor in the park mode.
 2. The electrical motor of claim 1, wherein the park disk is electrically isolated from the power wire during operation of the electrical motor in the at least one running mode with a relay that is normally open.
 3. The electrical motor of claim 2, wherein the relay is an electromechanical relay.
 4. The electrical motor of claim 2, wherein the relay is a solid-state relay.
 5. The electrical motor of claim 1, further comprising at least one running mode wire electrically coupling the electrical motor to a motor switch, the at least one running mode wire traveling from the electrical motor to the motor switch through a ferrite bead and through at least one inductor.
 6. The electrical motor of claim 1, further comprising at least one running mode wire electrically coupling the electrical motor to a motor switch, the at least one running mode wire being electrically coupled to the power wire with at least one filter capacitor.
 7. The electrical motor of claim 1, further comprising at least one running mode wire electrically coupling the electrical motor to a motor switch and a Faraday cage through which the at least one running mode wire travels after exiting the exterior of the housing.
 8. The electrical motor of claim 7, further comprising at least one filter capacitor within the Faraday cage, the at least one running mode wire running through the at least one filter capacitor.
 9. The electrical motor of claim 8, further comprising an EMI filter PC board having EMI filter caps thereon through which the at least one running mode wire travels after exiting the Faraday cage.
 10. The electrical motor of claim 1, further comprising a ground wire electrically coupling the park disk to ground, the ground wire exiting the housing and being exposed at the exterior of the housing, the park wire and the power wire being electrically coupled to the ground wire with RC filters.
 11. An electrical motor operable in at least one running mode wherein the electrical motor operates at a constant speed and operable in a park mode wherein the electrical motor dynamically parks, the electrical motor comprising: a housing; a rotating park disk within the housing and functionally coupled to a ground contact, a park contact, and a battery positive contact, the park disk configured to allow the electrical motor to dynamically park by operating the electrical motor in the at least one running mode until the park disk rotates to a park position such that the park disk is electrically coupled to the ground contact and the park contact and not electrically coupled to the battery positive contact; a park wire electrically coupling the park contact to a motor switch, the motor switch configured to selectively switch the electrical motor between the at least one running mode and the park mode, the park wire exiting the housing and being exposed at an exterior of the housing; and a battery positive wire electrically coupling the battery positive contact to a positive terminal on a battery, the battery positive wire exiting the housing and being exposed at the exterior of the housing, wherein the park disk is electrically isolated from the battery positive wire during operation of the electrical motor in the at least one running mode and the park wire is electrically connected to the battery positive wire through the park disk during operation of the electrical motor in the park mode.
 12. A method of operating an electrical motor operable in at least one running mode wherein the electrical motor operates at a constant speed and operable in a park mode wherein the electrical motor dynamically parks, the electrical motor comprising a housing with a rotating park disk therein configured to cause the electrical motor to dynamically park, a park wire electrically coupling the park disk to a motor switch, the motor switch configured to selectively switch the electrical motor between the at least one running mode and the park mode, the park wire exiting the housing and being exposed at an exterior of the housing, a power wire electrically coupling the park disk to a power source, the power wire exiting the housing and being exposed at the exterior of a housing, the method comprising: electrically isolating the park disk from the power wire during operation of the electrical motor in the at least one running mode; and electrically connecting the park wire through the park disk to the power wire during operation of the electrical motor in the park mode.
 13. The method of claim 12, wherein electrically isolating the park disk wire from the power wire includes providing a relay that is normally open between the park disk and the power wire.
 14. The method of claim 13, wherein the relay is an electromechanical relay.
 15. The method of claim 14, wherein electrically connecting the park wire to the power wire includes energizing the electromechanical relay.
 16. The method of claim 13, wherein the relay is a solid-state relay.
 17. The method of claim 12, further comprising providing a ferrite bead and at least one inductor on at least one running mode wire between the electrical motor and the motor switch, the at least one running mode wire electrically coupling the electrical motor to the motor switch.
 18. The electrical motor of claim 12, further comprising electrically coupling at least one running mode wire to the power wire with at least one filter capacitor, the at least one running mode wire electrically coupling the electrical motor to the motor switch.
 19. The electrical motor of claim 12, further comprising electrically coupling the park wire and the power wire to a ground wire with RC filters, the ground wire electrically coupling the park disk to ground and exiting the housing and being exposed to the exterior of the housing.
 20. The electrical motor of claim 12, further comprising providing a Faraday cage through which at least one running mode wire travels after exiting the exterior of the housing, the at least one running mode wire electrically coupling the electrical motor to the motor switch.
 21. The electrical motor of claim 20, further comprising providing at least one filter capacitor within the Faraday cage with the at least one running mode wire running through the at least one filter capacitor and providing an EMI filter PC board having EMI filter caps thereon through which the at least one running mode wire travels after exiting the Faraday cage.
 22. The electrical motor of claim
 12. 